This invention relates to the manufacture of parts of revolution by three-dimensional weaving capable of having a complex geometrical shape.
Woven parts of this type are used as reinforcement in the manufacture of hollow bodies of revolution obtained by the impregnation of such a part by means of a hardenable resin binder followed by machining to the precise dimensions desired for the hollow body. Such hollow bodies are used notably in the field of ballistic missiles and rockets.
A known method (U.S. Pat. No. 3,904,464) for making a hollow body of revolution, consists in fabricating, on a tool having the internal form of the part to be made, an "urchin" of radial pins in fibres and polymerized resin. These pins delimit longitudinal and circumferential "corridors" which are then, by simple winding, filled with resin-preimpregnated yarns. The assembly obtained is finally subjected to polymerization and then to machining and, if necessary, to reimpregnation under pressure followed by further machining.
This known method has the drawback of being long and complicated to implement, especially as regards the fabrication of the urchin which calls for many moulding, machining and glueing operations. Furthermore, the said method practically allows only the fabrication of parts having a simple geometrical form.
Another three-dimensional weaving method is described in the U.S. Pat. No. 3,834,424. That method requires a very complicated loom and does not lead to woven parts of revolution.
The French Pat. No. 73/14 956 describes, for its part, an apparatus for the fabrication by three-dimensional weaving of hollow parts of revolution of which the principle lies in the simultaneous helical laying, by means of a stitching head, of circumferential and radial yarns through a network of longitudinal rods made of polymerized resin fibre. This apparatus, although complicated, does not permit the fabrication of parts of complex form, but only cylindrical or, with great difficulties, conical parts.
Prior-art methods have, in addition to the indicated drawbacks, a drawback having to do with the quality of the parts obtained by three-dimensional weaving. This quality in fact depends directly on the fibre content of the woven parts and hence on the tamping during weaving. In prior-art methods, this tamping is obtained either manually or by the binding force induced by the tension of the circumferential yarns used. Tamping by binding force varies with the winding diameter, resulting in variations in the thickness of the part. In addition, in the case of large thicknesses, the binding force decreases from the inside toward the outside of the part, thus leading to a woven material which is heterogeneous in its thickness. The binding force also has a tendency to change the diameter of the courses laid, and this results in the slipping and shifting of fibres, harmful to final product quality.